1. Field of the Invention
The instant invention pertains to the treatment of polysaccharide ester films and more particularly to the production of clear polysaccharide ester films employing a solvent.
2. Description of the Prior Art
Cellulose acetate membranes are made up of a blend of cellulose acetate of varying degrees of acetate substitution. These membranes are produced in a way that will result in a highly porous matrix. With the proper blend of acetylated cellulose manufactured to the form of a highly porous matrix, one obtains a hydrophilic membrane capable of being employed for filtration or as a support media for an electrophoretic process.
To employ a cellulose acetate membrane in the electrophoretic process, one hydrates the membrane in an aqueous buffer and positions it in an electrophoretic cell. Once a sample has been applied to the surface of the membrane, a voltage potential is applied across the membrane to start the electrophoetic process. After a period of time, electrophoresis is terminated and the membrane is removed from the electrophoretic cell. The separated sample is detected by a chemical staining process to yield colored bands or spots on a white, opaque, cellulose acetate membrane background.
To quantitate the colored bands or spots, one must first transform the white opaque membrane into a clear, colorless film. This is known as the "clearing process" in electrophoretic methodology. The clearing process consists of the following steps. The membrane can be directly rinsed in a clearing solvent comprised of two fractions. Preferably, the membrane is first dehydrated in absolute alcohol and then rinsed in a clearing solvent comprised of two fractions. These rinsed membranes are placed on a suitable support, e.g., a glass plate, and dried, e.g., in an oven, at a suitable temperature, e.g., from about 70.degree. to about 100.degree. C. The dried cellulose acetate film is then removed from the support. This dried cellulose acetate membrane is now a clear, colorless cellulose acetate film still containing the colored bands or spots. These colored bands or spots can now be quantitated by scanning the clear cellulose acetate film with a densitometer or other suitable means. Therefore, the clearing process converts a non-transparent membrane into a transparent film to allow optical measurements to be performed upon substances located within the film.
The above described clearing process, as practiced in the prior art, employed as the clearing solvent one of the solutions set forth in Table I.
TABLE I ______________________________________ First Second Component Component ______________________________________ Alcohol* glacial acetic acid. Alcohol*: cyclohexanone. Water: N,N-dimethyl formamide. ______________________________________ *As used in this particular instance, the term "alcohol" encompasses methyl alcohol, ethyl alcohol, isopropyl alcohol, and mixtures thereof.
The solvents employed as the second component of the prior art solvents are relatively toxic as can be seen from the information set forth in Table II.
TABLE II.sup.1 ______________________________________ Solvent LD.sub.50.sup.2, mg/kg LCL.sub.o.sup.3 TWA.sup.4 ______________________________________ Cyclohexanone 1620.sup.5 2000 ppm/4H.sup.6 50 ppm N,N-dimethylformamide 2800.sup.5 N/L.sup.7 10 ppm Acetic Acid 3310.sup.5,8 1600 ppm/4H.sup.6 10 ppm ______________________________________ .sup.1 All data from Registry of Toxic Effects of Chemical Substances, Volume II, U.S. Department of HEW, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, Cincinnati, Ohio, 1977 Edition (September, 1977). .sup.2 For definition see ibid at page ix. .sup.3 For definition see ibid at page ix. .sup.4 For definition see ibid at page xi. .sup.5 Oral-rat .sup.6 Inhilation-Rat. .sup.7 N/L denotes not listed in Registry. .sup.8 Oral ingestion very serious; data listed for sodium acetate solution and not for acetic acid. See Patty, Industrial Hygiene and Toxicology, Vol II, 2nd Edition, Interscience Publishers, New York, N.Y. (1963).
Accordingly, for health and safety factors, it would be very desirable to be able to employ a less toxic solvent as the second component of a clearing solvent.